Thermoelectric motor in electron discharge device envelope



Jan. 11, 1966 p, CLARKE 3,229,177

THERMOELECTRIC MOTOR IN ELECTRON DISCHARGE DEVICE ENVELOPE I Filed Oct. 23, 1962 as n00 FlG.l.

INVENTOR: PETER J. CLARKE,

Y A M HI ATTORNEY.

United States Patent 3,229,177 THERMOELECTRIC MOTOR IN ELECTRON DISCHARGE DEVICE ENVELOPE Peter J. Clarke, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Oct. 23, 1962, Ser. No. 232,422 Claims. (Cl. 318-117) The present invention relates to electron discharge device vacuum enclosures of the permanently sealed or semipermanently sealed type, and to means for providing mechanical motion in suchevacuated environment under control from outside the evacuated environment. More particularly the invention relates to improved means utilizing electric power for providing mechanical drive of a rotatable member in an environment evacuated to a degree suitable for electron beam formation and utilization.

Information display systems are known which involve modulation of the brightness, or color and brightness, of light by variation of the light diffractive action of a thin layer or film of a viscous fluid medium in accordance with a pattern of electric charge formed thereon under the control of information signals. One information display system utilizing this principle is described in the US, patent to W. E. Glenn, Reissue 25,169, commonly assigned herewith.

One of the problems in the operation of such information display systems employing charge-deformable media is that in order to obtain a lengthened operating life it is desirable to continually renew the surface of the deformable medium exposed to the charge deposition action, and hence some means is desired for slowly but continuously moving a fresh layer of the deformable medium into the area or field where the charge deposition action takes place. It has further been found that the rate at which a fresh surface or layer of the deformable medium can be advanced into the charge deposition area, in order to avoid undesired variation in light modulating properties of the medium, is very low, being of the order of, for example, one inch per hour of operating life. It is also desirable of course to take maximum advantage of this low permissive rate of surface renewal so as to conserve the total quantity of deformable medium required for a given operating lifetime.

To produce such movement of the deformable fluid layer various systems have been contemplated, such as embodiments whereby the deformable medium is a liquid and is pumped or otherwise slowly flowed in a film of desired thickness across a stationary supporting substrate, and embodiments whereby a supporting substrate bearing a suitable layer of the deformable medium is itself moved so as to bring a fresh surface into the area where charge deposition takes place.

However the foregoing unusual requirements render conventional driving means unsuitable, particularly from the standpoint of obtaining desired long operating life of the order of several thousand hours. Electric motors of the stator and rotatable rotor type disposed within the vacuum environment are undesirable, for example, because of the difficulty of sufficiently outgassing the evacuated environment to avoid later contamination of the vacuum by gases gradually evolved from the various parts of the motor. Moreover the gases and other contaminants produced from lubricants in such an electric motor as Well as the minute particles of metal or other foreign matter generated by the mechanical wear of moving parts during a prolonged operating life, limit the practicality of such driving mechanisms. Mechanical drives involving shafts or other mechanical couplings extending through the Wall of the vacuum enclosure are ice impractical because of the difiiculty of maintaining an adequately vacuum-tight seal for such wall-penetrating members during lengthy operating life. Driving arrangements employing magnetic coupling are undesirable because of the interaction between the stray magnetic fields they involve and the inherently magnetic field-sensitive process of electric charge deposition on the deformable medium.

Accordingly it is a principal object of the present invention to provide an improved driving means suitable for producing, in an evacuated environment of the above character, externally controllable mechanical motion sufficient to provide continual renewal of a layer of a deformable viscous fluid medium in an electrostatic charge deposition area, at desired rates.

Another object is to provide driving means of the foregoing character which is mechanically simple, dependable, inexpensive, capable of operating for prolonged periods without breakdown or need for repairs, and easily controllable in speed from outside the vacuum enclosure.

Another object is to provide electrically powered driving means for producing mechanical movement in an environment evacuated to a degree suitable for the emission of electrons from a cathode, and the formation and utilization of electron beams, and whose parts disposed in the evacuated environment are relatively inexpensive and easily outgassed prior to scaling.

These and other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawing wherein:

FIGURE 1 is a schematic illustration of an information display system with which the present invention is particularly suitable;

FIGURE 2 is an enlarged diagrammatic elevation view of one form of driving means constructed in accordance with the present invention; and

FIGURE 3 is a plan view of the structure shown in FIGURE 2.

Referring to the drawing FIGURE 1 is a schematic representation of an information display system of a type with which the present invention is particularly suitable. An envelope 2 forms a vacuum enclosure within which an electron beam, generated by an electron gun 4 and controlled in intensity and deflection by appropriate control signals supplied to the terminals 6, 8, 10, is caused to deposit a desired pattern of electric charge on a film or layer of a deformable viscous fluid medium 12 carried by a moveable substrate shown as a rotatable disc 14. The charge deposition or raster area on the disc is shown at 16. As described in detail in the aforementioned Reissue Patent 25,169 to W. E. Glenn, a suitable optical system is provided for projecting light from a source 20 through the deformable medium 12, the deformable medium providing a variable light dilfractive action under the control of deposited electric charge. A cooperating schlieren optical system including a set of input bars and slits 24, a set of output bars and slits 28, a converging lens 32 and an output projection lens 36 serves to reproduce on a screen 40 an image corresponding to the information placed by electric charge deposition on the deformable medium 12.

As previously stated in an information display system of the type illustrated in FIGURE 1 it has been found desirable to continually renew the film or layer 12 of deformable fluid medium in the electric charge deposition or raster area 16, and for this purpose, when as shown the deformable fluid is supplied in a liquid state, the disc 14 is arranged for rotation in a pool 44 of the deformable medium contained within a cup 48 and of such depth as to immerse a substantial portion of the lower half of the disc 14. Thus rotation of the disc 14 coats the immersed portion with the deformable medium 12 and continually moves a freshly coated portion of the disc 14 into the electric charge deposition area 16.

For driving the disc 14 or other equivalent deformable medium renewing means in accordance with the present invention I provide driving means including a rotor or rotatable member 52 which may be a shaft, capstan or drum suitably supported for rotation about a fixed axis 54, and mechanically drivingly connected, for example directly as shown in FIGURE 1, to disc 14. In accordance with the invention there is wound around the rotatable member 52 a plurality of driving members, 56,

58, shown as two in number, of continuous elongate substantially stretch-free metallic material such as metal wires or wire ropes. Each of the driving members 56, 58 may be wound on drum 52 more or less than one complete turn. One end of wire 56 is anchored to a non-resilient support 60 while its other end is connected to a yieldable tensor such as a tension spring 64 arranged to provide a continuous tension force on the wire 56. Other tensioning means may be used to provide the function of the yieldable tensor 64, such as a weight hung on wire 56 or a resilient cantilever support. One end of wire 58 is anchored to a stationary support 70 while its other end is connected to a stationary support 72 through a yieldable tensor such as tension spring 74. When in an unheated state, each wire 56, 58 is maintained in appreciable tension by its respective spring 64, 74 so as to tightly grip drum 52.

Provision is made for intermittently slackening by thermal expansion in a selected sequence under control of switch 84, the portion of each wire extending between the drum 52 and its non-resiliently anchored end. In the illustrative embodiment shown, the thermal slackening is achieved by employing each wire 56, 58 itself as a temperature responsive element, as by passing an electric resistance heating current from a potential source 86 directly through the portion of each wire. Alternatively, however, other temperature responsive means for slackening the wires may be employed, such as temperature responsive movement of supports 66, 70.

Source 86 is connected to the anchored end 88 of wire 56 through terminal 90 of switch 84 and lead 92, and to the anchored end 94 of wire 58 through terminal 96 of switch 84 and lead 98. Lead 100 is a common return to potential source 86. Potential source 86 and switch 84 may be disposed outside the vacuum environment in which the rotatable member 52, driving wires 56, 58 and supports 60, 62, 70, 72 are situated, with the resulting connection through the wall 2 of the vacuum environment being limited to lead 92, 98, and 100 whose passage through the wall of the vacuum enclosure may be per- ;manently sealed in accordance with known techniques.

Operation of the apparatus shown in FIGURES 2 and 3 will now be described. As switch 84 is thrown to pass current through and heat section 102 of wire 56, this portion will expand and at least some of the slack will be taken up in contractual movement of the yieldable tensor, spring 64. During expansion of wire 56 no movement of drum 52 results because drum 52 is held stationary by the relatively tight grip of wire 58. The switch 84 is then thrown to contact 96 to terminate heating of wire 56 and pass current through and begin heating of section 104 of wire 58. Section 102 of wire 56 then begins to cool and contract, and as it contracts and cinches tight about the drum 52 it applies a torque to drum 52 in the direction of arrow 110 in FIGURE 1. The force supplied by the contraction of section 102 of wire 56 is greater than the force applied by spring 64. Since section 104 of wire 58 starts to expand at about the same time due to its heating, and wire 58 loosens about the drum 52, the net torque exerted by wire 56 in direction of arrow 110 is greater than any restraint exerted by wire 58, and drum 52 is given a small rotation in direction of arrow 110.

When the switch 84 is thrown back to terminal 90, section 104 of wire 58 starts to cool and contract and cinches tight about drum 52, while at the same time the expansion of section 102 loosens wire 56 about the drum producing a net torque exceeding the force of spring 74, and again causing a slight rotation of drum 52 in the direction of arrow 110.

Thus it may be seen that the drum 52 will continue to rotate in small increments in a counterclockwise direction as shown in FIGURE 2, as long as the temperature responsive elongation effect is switched from one wire to the other. The angular amount of each increment of rotation of drum 52 depends upon the geometry involved, that is the diameter of the drum 52 relative to the amount of temperature responsive elongation of the wire involved, which in the embodiment illustrated depends of course upon the heatable lengths and thermal coefficient of expansion of the wires involved. I have found for example that using heatable sections of nichrome ribbon approximately 30 mils by 5 mils in cross section and about three inches long, and with a drum 52 diameter of inch, drum rotations of 0.5 revolution per hour can be obtained with a source 86 of 1.7 volts at 1.0 amperes DC. and switching at switch 84 at a rate of eight cycles per minute.

The choice of metal for the driving wires 56, 58 is not critical. Any suitable metal of suflicient tensile strength such as nickel, or stainless steel, or nichrome may be employed, although desirably the composition of the driving wires should be such as to minimize evolution of gas into the evacuated environment within enclosure 2 during prolonged operating life. For convenience electrical contact between the driving wires 56, 58 and the drum 52 eliminates the need for a separate commutator for lead 100, but if direct electrical contact between the wires and drum is impossible or undesirable a separate commutator (not shown) may be required to provide electrical contact between the wires 56, 58 and lead 100.

It is within the contemplation of the present invention that a greater number than the two driving wires 56, 58 shown in FIGURES 2 and 3 may be employed if desired. For example several pairs of such wires may be operated in parallel, or if desired a plurality of wires may be chosen to perform the function of wire 56 and another plurality of wires may be chosen to perform the function of wire 58, the number of wires in each such plurality not necessarily being required to be equal. Moreover a single wire may be employed provided suitable alternate means, such as a ratchet (not shown) is provided to prevent reverse rotation of the drum 52 during the non-driving portion of the slackening-tightening cycle of the single wire, and where the resultant intermittent nature of the driving force is not objection able. Moreover smoother motion of the driven member 52 may be obtained by using several sets of wires with different time rates of thermal excursion. For example if two pairs of wires were used, one pair having an associated thermal excursion cycle of seven seconds then the two pairs would supply torque in phase only every 28 seconds.

Driving means of the foregoing character has many advantages. It will be evident that a driving means constructed in accordance with the present invention is mechanically simple, relatively inexpensive, sturdy and capable of taking up little space. Moreover the amount of mechanical relative movement of parts is extremely limited so as to minimize wear, and presence of lubricants is avoided. Further, the driving means is completely compatible with the degree of vacuum required, e.g. 10- of Hg, for electronic emission and formation and utilization of electron beams, and with the requirement of the preliminary bakeout or outgassing heat treatment desirable to insure a minimum of evolved gas in the evacuated environment during subsequent operationfor a prolonged life of several thousand hours.

It will be appreciated by those skilled in the art that the invention may be carried out in various ways and may take) various forms and embodiments other than the illustrative embodiments heretofore described. Accordingly it is to be understood that the scope of the invention is not limited by the details of the foregoing description, but will be defined in the folowing claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electron discharge device envelope containing a rotor adapted to be driven, driving means comprising an elongate flexible member, yieldable tensor means connected to the flexible member for urging an intermediate portion of the flexible member in one direction and for yielding to permit moving of said intermediate portion of said flexible member in the other direction, said intermediate portion of said flexible member being in frictional driving engagement with said rotor, means for impeding rotation of said rotor during movement of said flexible member in one of said directions, and thermal means for intermittently advancing said flexible member in said one direction and retracting said flexible member in said other direction.

2. In an electron discharge device envelope containing a rotor adapted to be driven, driving means comprising a longitudinally extending wire, yieldable tensor means connected to the wire for moving an intermediate portion of the wire in one direction responsive to slackening of the wire and for yielding to permit moving of said intermediate portion of said wire in the other direction responsive to tautening of the wire, said intermediate portion of said wire being trictionally drivingly engageable with said rotor, means for preventing rota-tion of said rotor during movement of said wire in one of said directions, and thermal means for intermittently slackening and tautening said wire.

3. In an electron discharge device envelope containing a rotor adapted to be driven, driving means comprising a longitudinally extending wire, yieldable tensor means connected to the wire for moving an intermediate portion of the wire in one direction responsive to slackening of the Wire and for yielding to permit moving of said intermediate portion of said wire in the other direction responsive to tautening of the wire, said intermediate portion of said wire being frictionally engageable with said rotor, means for preventing rotation of said rotor during movement of said wire in one of said directions,

means for directly heating and thermally elongating said Wire to permit slackening thereof, and means for intermittently interrupting said heating means to permit cooling and tautening thereof.

4. In an electron discharge device including an evacuated envelope containing a rotor adapted to be driven, driving means comprising a pair of longitudinally extending wires, yieldable tensor means connected to one end of each wire for moving an intermediate portion of either wire in one direction relative to said rotor responsive to slackening of the respective wire and for yielding to permit moving of the intermediate portion of either wire in the other direction responsive to tautening of the respective wire, said intermediate portion of each wire being frictionally engageable with said rotor, means for preventing rotation of said rotor during movement of either wire in one of said directions, and means including a control external to said envelope for intermittently thermally slackening said wires in alternation.

5. In an evacuated environment containing a rotor adapted to be driven, driving means comprising an elongate flexible member anchored at one of its ends, a yieldable tensor engaged with the other end of said elongate member for applying a continuous tensioning force thereto, an intermediate portion of said elongate member being frictionally engageable with said rotor so as to exert a torque thereon responsive to a longitudinal movement of said intermediate portion, temperature sensitive means for producing a slackening of the portion of said elongate member between the rotor and the anchored end of said elongate member responsive to change in the temperature of said temperature sensitive means in one direction, whereby said slackening produced by said temperature change is taken up by contractual movement of said tensor and said elongate member is advanced in one direction relative to said rotor, means for preventing rotation of said rotor during said relative advancing movement of said elongate member in said one direction, whereby responsive to change of temperature of said temperature sensitive means in the other direction said elongate member retracts in the other direction and thereby rotates said rotor.

6. In an evacuated environment containing a rotor adapted to be driven, driving means comprising an elongate flexible member, anchored at one of its ends, a yieldable tensor connected to the other end of said elongate member for applying a continuous tensioning force thereto, an intermediate portion of said elongate member being frictionally drivingly engageable with said rotor so as to exert a torque thereon responsive to a longitudinal movement of said intermediate portion, temperature sensitive means for producing an alternate slackening and tautening of the portion of said elongate member between the rotor and the anchored end of said elongate member responsive to change in the temperature of said tempera ture sensitive means, whereby said slackening produced by said temperature change is taken up by contractual movement of said tensor and said elongate member is moved in one direction relative to said rotor and said tensor yields to permit movement of said elongate member in the other direction relative to said rotor during tautening of said elongate member, and means for preventing rotation of said rotor during movement of said elongate member in one of said directions.

7. In combination with an electron discharge device having an envelope forming a vacuum chamber, a rotatable drum mounted for rotation in the vacuum chamber, a first wire having a central portion wound around the drum, a stationary support to which one end of said first wire is connected and a resilient support to which the other end of said first wire is connected, a second wire having a central portion wound around the drum, a stationary support to which one end of said second wire is connected and a resilient support to which the other end of said second wire is connected, each of said wires having a length such that when in the relatively unheated state its end portions are taut and its central portion tightly grips said drum, the wound portion of each of said wires being so oriented on said drum that each wire extends from said drum to its stationary support in a tangential direction corresponding to a common direction of drum rotation, and means including a control external to said vacuum chamber for intermittently supplying heat alternately to the segments of said first and second wires extending from the drum to said stationary supports.

8. In an electron discharge device including a drum adapted to be driven, driving apparatus comprising a first elongate heat expansible metal member yieldably anchored at one end and non-yieldably anchored at its other end and having its central portion wound at least partially around the drum, a second elongate heat expansible metal member yieldably anchored at one end and non-yieldably anchored at its other end and having its central portion wound around the drum, each of said elongated metal members having a length such that when in the relatively unheated state its end portions are taut and its central portion tightly grips said drum, and means for alternately heating the segments of said first and second elongate metal members which extend away from the drum in the direction of drum rotation desired.

9. In combination with an electron discharge device having an envelope forming a vacuum chamber, a rotatable drum mounted for rotation in the vacuum chamber and adapted to be driven, a first elongate heat expansible metal member yieldably anchored at one end and nonyieldably anchored at its other end and having its central portion wound around the drum, a second elongate heat expansible metal member yieldably anchored at one end and non-yieldably anchored at its other end and having its central portion wound around the drum, each of said elongate metal members having alength such that when in the relatively unheated state its end portions are taut and its central portion snugly grips said drum, and means including a switch external to said vacuum chamber for passing an electrical resistance heating current alternately through the segments of said first and second elongate metal members which extend away from the drum in the direction of drum rotation desired.

10. In an electron discharge device including a rotatable drum adapted to be driven, driving apparatus comprising a first elongate heat-expansible metal wire having a central portion wound around the drum, a stationary support to which one end of said first Wire is connected and a resilient support to which the other end of said first wire is connected, a second elongate heatexpansible metal wire having a central portion wound around the drum, a stationary support for one end of said second wire and a resilient support to which the other end of'said second wire is connected, each of said elongate metal wires having a length such that when in the relatively unheated state its end portions are taut and its central portion tightly grips said drum, the Wound portion of each of said wires being so oriented on said drum that the portions of said wires between said drum and said stationary supports extend from said drum in a direction corresponding to a desired direction of drum rotation, and means for alternately heating the segments of said first and second wires extending from the drum to said stationary supports.

References Cited by theExaminer UNITED STATES PATENTS 954,682 4/1910 Low et a1. 60-23 1,804,709 5/1931 Shoenberg. 2,379,730 7/1945 Longerich 313-451 X GEORGE N. WESTBY, Primary Examiner.

ROBERT SEGAL, Examiner. 

1. IN AN ELECTRON DISCHARGE DEVICE ENVELOPE CONTAINING A ROTOR ADAPTED TO BE DRIVEN, DRIVING MEANS COMPRISING AN ELONGATE FLEXIBLE MEMBER, YIELDABLE TENSOR MEANS CONNECTED TO THE FLEXIBLE MEMBER FOR URGING AN INTERMEDIATE PORTION OF THE FLEXIBLE MEMBER IN ONE DIRECTION AND FOR YIELDING TO PERMIT MOVING OF SAID INTERMEDIATE PORTION OF SAID FLEXIBLE MEMBER IN THE OTHER DIRECTION, SAID INTERMEDIATE PORTION OF SAID FLEXIBLE MEMBER BEING IN FRICTIONAL DRIVING ENGAGEMENT WITH SAID ROTOR, MEANS FOR IMPEDING ROTATION OF SAID ROTOR DURING MOVEMENT OF SAID FLEXIBLE MEMBER IN ONE OF SAID DIRECTIONS, AND THERMAL MEANS FOR INTERMITTENTLY ADVANCING SAID FLEXIBLE MEMBER IN SAID ONE DIRECTION AND RETRACTING SAID FLEXIBLE MEMBER IN SAID OTHER DIRECTION. 